2. [20 points] (1) Make schematic drawings of the Bravais lattices for the following atom arrangements (in two dimension). O O O O O O O O O O O O O O O O O OOO OOOO O O O O O O O O Two different type of atoms (b) Draw the reciprocal lattice for the 2D Bravais lattice obtained in (a), based on which draw the first Brillouin zone. 2. [10 points] Consider a one-dimensional -A-B-A-B-A-B- atomic chain formed by two type of atoms A and B form a line. The distance between neighboring A and B atoms is AB = a/3 and BA = 2a/3, as shown below. The atomic form factor is fa and fe, respectively, for atoms A and B. The incident x-ray beam is perpendicular to the line. Calculate the geometric structure factor and find the condition of systematic absence. a/3 2a/3